This invention relates to plastic housings for electronic components, and more particularly, to such plastic housings which provide static charge protection to the electronic components. The invention further relates to a method of fabricating static charge protective plastic housings for electronic components.
It is desireable to provide low-cost housings for electronic components such as plastic cases for electronic watches and calculators. However, electronic components are subject to temporary or permanent damage caused by static charge. MOS integrated circuits, for example, are subject to permanent damage from static charge. Static charge will cause an I.sup.2 L bipolar integrated circuit, on the otherhand, to lose the present information contained therein although the static charge will not normally cause permanent damage. Even so, a plastic housing would be unsuitable for electronic watches or calculators which are frequently handled, since static charge could cause inaccurate time or calculations, respectively.
It is therefore an object of the present invention to provide an improved plastic housing for electronic components.
It is another object of the invention to provide plastic housings for electronic components which protect the electronic components from static charge.
It is a further object of the invention to provide low-cost plastic housings for electronic components which protect the electronic components from static charge and yet are corrosion resistant.
Another object of the invention is to provide a method of manufacturing static charge protective plastic housings for electronic components.
Yet another object of the invention is to provide a method of fabricating static charge protective plastic housings for electronic components which housings are corrosion resistant.
It is still a further object of the invention to provide a method of fabricating plastic housings with dual-metal coatings in a single ion plating chamber.
These and other objects are accomplished in accordance with the present invention in which plastic housings for electronic components are coated with a first layer of conductive metal and overcoated with a second layer of corrosion-resistant metal. In a preferred embodiment, the housing is interiorly coated by ion plating a first layer of a low-cost, highly-conductive metal, such as copper, and then overcoated by ion plating a layer of corrosion-resistant metal, such as nickel or chrome. The copper layer provides static protection for the electronic component to be contained within the housing while the nickel layer provides chemical corrosion resistance and mechanical hardness and toughness for the copper layer. In a preferred method of fabricating the plastic housings, the plastic parts, which are formed by injection molding or some other well-known technique, are placed in an ion plating chamber containing charges of both copper and nickel in preselected amounts. During the heating cycle, the copper melts first, wets the tungsten filaments and evaporates into a plasma which is deposited on the plastic parts. The heat of evaporation and electrical conductivity of the copper hold the temperature of the filaments below that which is required to vaporize the nickel until almost all of the copper has been plated. Then, as the temperature of the filaments rise, the nickel is vaporized into the plasma and is plated onto the parts. The resulting coating starts as pure copper, then grades into almost pure nickel.